Please follow this instruction
to create and manage mail group. If the issue still persists, contact our ONLYOFFICE Support Team
and specify the following:
1) The name of the portal, where the problem occurs;
2) The concrete action you are trying to perform on your portal;
3) The step-by-step scenario of your actions;
4) The concrete moment the problem occurrs in;
5) Whether only you are facing this problem or some other users \ all the users of your portal.
Also, please, send us the screenshot which illustrates the issue mentioned.
Looking forward to your answer.